Calibrating active forces of gliding bacteria through self-buckling

Abstract. Self-buckling, first described in 1778 by Leonard Euler, is the buckling of a flexible column under its own weight if its length exceeds a critical value. Here we transfer the principle of self-buckling to gliding filamentous cyanobacteria, one of the oldest lifeforms on earth with manifold potential applications in economics and ecology. These phototrophic organisms form long and flexible filaments that actively glide over solid surfaces. However, the force generation mechanism of their gliding apparatus is not yet understood. We quantify their propulsion forces by systematic self-buckling experiments: Filaments that glide onto an obstacle buckle if their body length exceeds a certain critical value. Adapting Euler’s self-buckling theory to the properties of self-propelling filaments, we derive the active force density from the critical length and an independent calibration of the bending rigidity. Our results indicate that self-buckling also plays a crucial role in natural habitats. In conjunction with polydisperse length distributions and stimuli-dependent propulsion forces, rich structures emerge, enabling colonies to adapt to an ever changing environment.

Keywords: Gliding motility, filamentous cyanobacteria, self-buckling, active matter